What happens when I eat prebiotics?
Prebiotics are non-digestible food ingredients that stimulate the growth and activity of our intestinal bacteria. Since they have several beneficial effects on the gut health, such as microbiota support and immune system modulation, they have far reaching effects on our overall health and well-being. This article summarizes the route through the digestive system and the end benefits that can be obtained through ingestion of prebiotics and prebiotic supplements.
The journey of prebiotics from the mouth to the intestines
Prebiotics do not get absorbed in the mouth. Instead, they journey through the gastrointestinal tract (1) until they reach the large intestine, where they are fermented by the gut microbiota. Here is a breakdown of their journey:
The journey of prebiotics from the mouth to the intestines typically involves the following steps (2):
- Ingestion – Prebiotics are consumed as part of the diet through various high fibre food sources.
- Passage through the stomach – Once ingested, prebiotics pass through the stomach where they are exposed to gastric acids and enzymes. However, they are not broken down or absorbed in the stomach.
- Transit through the small intestine – Prebiotics go into the small intestine where they may undergo minimal digestion by enzymes. Those enzymes are produced by the pancreas, However, the majority of the prebiotics remain intact as they are not broken down by human digestive enzymes.
- Fermentation in the large intestine – The undigested prebiotics reach the large intestine, which is also called the colon. There they serve as a substrate for fermentation by the gut microbiota.
- Absorption of fermentation byproducts.
These 2 beneficial bacteria play a major role in the fermentation of prebiotics
Two key types of beneficial bacteria in the gut are Bifidobacteria and Lactobacilli, which can be significantly stimulated by galacto-oligosaccharides (GOS). GOS are a type of prebiotic fiber made up of short chains of galactose molecules connected by glycosidic bonds, derived from lactose (3).
Bifidobacteria are anaerobic bacteria that predominantly reside in the human colon and are one of the most abundant genera in the gut microbiota (4).
Lactobacilli, also Gram-positive bacteria, are commonly found in the human gastrointestinal tract (5). Both Bifidobacteria and Lactobacilli contribute to gut health by aiding digestion, supporting immune function, and inhibiting the growth of harmful bacteria. Research indicates that certain strains of Lactobacilli offer additional health benefits, such as reducing the risk of antibiotic-associated diarrhea, alleviating symptoms of irritable bowel syndrome (IBS), and promoting vaginal health in women (4, 5).
What are prebiotics doing in the intestines?
When prebiotics reach the colon, Bifidobacteria, Lactobacilli, and other gut bacteria possess enzymes capable of breaking down the carbohydrates in prebiotics—something human digestive enzymes cannot do.
As prebiotics are fermented by these bacteria, they produce various metabolites, mainly short-chain fatty acids (SCFAs) like acetate, propionate, and butyrate. These SCFAs play a vital role in maintaining gut health and offer numerous benefits to the body. Additionally, fermentation generates gases such as hydrogen, methane, and carbon dioxide, which can affect gut motility and lead to bloating and flatulence in some individuals (6).
SCFAs are absorbed into the bloodstream via the colon lining and travel to various tissues and organs. In particular, they reach the liver, where they can be metabolized or used as an energy source.
Butyrate is especially important for colonic health, serving as the primary energy source for colon cells (colonocytes) and helping maintain a healthy gut barrier (7).
Acetate and propionate have also been shown to influence metabolic processes and may play a role in regulating glucose and lipid metabolism (8).
Conclusion
In conclusion, Bifidobacteria and Lactobacilli are essential gut bacteria that promote digestive health, immune function, and inhibit harmful pathogens. Prebiotics stimulate these bacteria, leading to the production of SCFAs such as butyrate, acetate, and propionate. These SCFAs support gut health, influence metabolic processes, and contribute to overall well-being.
